Converter vessels in which molten metal is refined into steel are lined with refractory material in order to protect the vessel walls against the effects of the extremely high temperatures experienced during the refining process. The refractory material is conventionally comprised of a pitch-bearing basic aggregate such as periclase (MgO) or the like.
It is necessary in such practice, to preheat newly installed refractory material, commonly called "burn-in", in order to coke the carbon element in the pitch thus to prepare the refractory lining to resist slag and metal attack by closing the joints. The rate at which heat is applied must be controlled in order to prevent spalling of the refractory material or other adverse affects. Burn-in of the lining is also desirable in order to prevent severe thermal shock to the refractory which would result upon charging molten iron from a blast furnace to a converter having a cold, newly installed lining. Yet another reason for burning in a newly installed converter lining is to avoid severe and unpredictable temperature losses during the initial heats processed in the converter following relining caused by the excessive transfer of heat from the melt to the cold, newly installed material.
In a conventional top-blown oxygen converter, commonly referred to as a BOP converter, burn-in is readily accomplished by placing a carbonaceous material, such as wook or coke, in the converter bottom and burning this combustible material with a controlled rate of oxygen from the oxygen lance. By controlling the rate of oxygen flow through the lance, a definite rate of heating of the lining is accomplished.
In the bottom-blown steelmaking converter in which the process known as Q-BOP is practiced, one or more tuyeres are provided in the bottom of the vessel through which jacketed oxygen and other gases or particulate fluxes are blown upwardly into the melt to be refined. The tuyeres each comprise a pair of concentrically disposed pipes forming two concentrically spaced passages. The axial passage is adapted to pass oxygen and other refining materials while the annulus passes the jacketing gas which is a gaseous hydrocarbon, such as propane or natural gas.
The tuyeres in Q-BOP converters are normally mounted in a bottom plug within a monolithic or brick formed refractory matrix. Because the refractory employed as the matrix has a shorter operating life than that which lines the converter walls it is the practice to form the plug as a removable member such that the same can be readily replaced at intervals during the lifespan of the wall lining. Obviously, it is necessary to burn-in the refractory of each bottom plug prior to reinstating the converter to use.
Burn-in of the refractory material in a Q-BOP converter, both that which lines the converter walls and that which forms the matrix of the bottom plug, is a time-consuming and expensive proposition. Since no suspended oxygen lance is available, the procedure employed in BOP practice cannot be used. As an alternative therefore, it has been the practice to employ a special gas-oxygen burner which is suspended into the interior of the converter through the mouth thereof. While this method of burning-in the refractory has proved satisfactory from the standpoint of the affect produced in the material, it cannot be accomplished with the tuyeres completely in place due to the possibility of pitch or foreign particulate matter entering the tuyere passages to plug the same or the complex arrangement of tubes that are operatively connected to the tuyeres. Accordingly, procedures heretofore employed with Q-BOP converters have required that only the outer pipe be installed in the refractory bottom plug when burn-in is conducted. Following burn-in this pipe is cleaned and the inner pipe thereafter installed before operation of the converter is reinstated. While such a procedure may not be overly arduous when practiced on small converters, it is extremely difficult and time consuming to perform on large bottom-blown converters due to the difficulty encountered in making the installation completely leak-proof. Typically the time required to burn-in refractories by this method has been 10 to 20 hours when a new bottom plug is installed together with a new wall lining and 10 to 16 hours when the plug is installed in an existing lining.
It is to the improvement of such procedures therefore that the present invention is directed.